A new species of polymorphic and colourful arboreal snail belonging to the family Camaenidae is described from Rotti Island (off southwestern end of Timor), southeastern Indonesian Archipelago. Amphidromus (Syndromus) rottiensis new species is diagnosable using shell morphology and geographically close congeners of the subgenus Syndromus, namely A. (S.) contrarius MÃ¼ller, 1774 and A. (S.) poecilochrous Fulton, 1896 are used for comparison. The new species being described here appears distinct enough to justify a specific status, and suggests an ancestral affiliation closest to A. (S.) contrarius and A. (S.) poecilochrous.